Hydrostatic machine valve biasing system

ABSTRACT

A hydrostatic pump or motor unit having a rotating cylinder biased into contact with a valve surface in proportion to separating forces to maintain sealing contact without excessive pressure. In an axial piston type hydrostatic unit, the rotating cylinder block engaging a fixed annular valve plate and the swash plate reciprocate the pistons in the cylinders to deliver fluid from the cylinders through the valve plate. A biasing motor between the cylinder block and a member axially fixed relative to the valve plate and a control system to provide a biasing control pressure provides a biasing force varying as a function of the separating force between the valve plate and cylinder block. In one arrangement the biasing motor has an internal cylindrical surface on the cylinder block and an external cylindrical surface on a fixed portion of the housing with a pair of annular pistons therebetween, one engaging in abutment on the cylinder block and the other engaging in abutment on the fixed housing portion to form a motor chamber supplied with biasing control pressure fluid to provide an auxiliary bias proportional to this pressure. In another arrangement the inner cylindrical surface is formed on the shaft rotating with the cylinder block. The biasing control system in one modification provides a biasing pressure proportional to speed and in another modification proportional to speed, power system pressure and displacement. A one or two step speed governor is mounted in the cylinder block.

United States Patent [19] Week et a1.

[451 May 14,1974

1 1 HYDROSTATIC MACHINE VALVE BIASING SYSTEM [75] Inventors: Nils P. Week, Allen Park; Carl E.

Shellman; Erkki A. Koivunen, both of Livonia, all of Mich.

[73] Assignee: General Motors Corporation,

Detroit, Mich.

[22] Filed: Aug. 7, 1972 [2]] Appl. No.: 278,443

[52] U.S. C1 417/213, 91/485, 91/487 [51] Int. Cl. F04b 49/00 [58] Field of Search 91/485, 487, 506; 417/213,

[56] References Cited UNlTED STATES PATENTS 3,618,471 11/1971 Hein et a1. 91/485 3,110,267 11/1963 Vetter 91/485 2,987,006 6/1971 Bowers et a1. 91/485 3,289,606 12/1966 Bosch 91/485 3,410,220 11/1968 Kratzenberg et a1. 91/485 2,388,644 11/1945 Roessler 91/485 1,817,080 8/1931 Howard l/485 3,168,009 2/1965 Grad 91/485 Primary ExaminerWilliam L. Freeh Assistant Examiner-Greg0ry Paul LaPointe Attorney, Agent, or Firm-A. M. Heiter [5 7] ABSTRACT A hydrostatic pump or motor unit having a rotating cylinder biased into contact with a valve surface in proportion to separating forces to maintain sealing contact without excessive pressure. In an axial piston type hydrostatic unit, the rotating cylinder block engaging a fixed annular valve plate and the swash plate reciprocate the pistons in the cylinders to deliver fluid from the cylinders through the valve plate. A biasing motor between the cylinder block and a member axially fixed relative to the valve plate and a control system to provide a biasing control pressure provides a biasing force varying as a function of the separating force between the valve plate and cylinder block. In one arrangement the biasing motor has an internal cylindrical surface on the cylinder block and an external cylindrical surface on a fixed portion of the housing with a pair of annular pistons therebetween, one engaging in abutment on the cylinder block and the other engaging in abutment on the fixed housing portion to form a motor chamber supplied with biasing control pressure fluid to provide an auxiliary bias proportional to this pressure. In another arrangement the inner cylindrical surface is formed on the shaft rotating with the cylinder block. The biasing control system in one modification provides a biasing pressure proportional to speed and in another modification proportional to speed, power system pressure anddisplacement. A one or two step speed governor is mounted in the cylinder block.

30 Claims, 10 Drawing Figures PATENTEUIAY 14 1924 SHEET 2 BF 5 NwN mmw

msmsum 14 m E 3.810.715

SHU b ii? 5 RESERVOIR r f F 552 X 295 SUPERCHARGE .292 PUMPAND EGULATOR GOVERNOR MOTO R 545 b 34 4 DISPLACEMENT 568 569 CONTROL VALVE/ b 592 C BIAS CONTROL VALVE HYDROSTATIC MACHINE VALVE BIASING SYSTEM This invention. relates to hydrostatic transmissions and converters and particularly to a biasing system for holding a cylinder in proper sealing contact during relative rotation with the valve plate of a hydrostatic pump or motor unit.

In hydrostatic converters such as the pump and motor units employed in hydrostatic transmissions, a cylinder moves relative to a valve plate having high and 'low pressure ports in order to alternately connect the cylinder opening to these ports during relative rotation of the cylinderand valve plate. In order to maintain optimum performance and efficiency the cylinder and valve plate are biased toward each other with a controlled bias force to obtain a minimum total of hydraulic leakage losses and friction losses throughout the full range of operation of the hydrostaticunit. Thus we propose by providing an improved biasing control system to increase the operating range with optimum efficiency and to increase its component ranges, the speed range, the differential pressure range and the variable displacement range. 1

In axial piston hydrostatic machines, the bias balance of the cylinder block into contact with the valve plate is critical. If the cylinder block bias is insufficient, excessive leakage, an efficiency loss, will occur at the interface between the cylinder block and valve plate and there may be complete lift-off resulting in a loss of pressure or power. If, on the other hand, a bias force is too large, the friction or efficiency losses due to relative rotation at the interface between the cylinder block and the valve plate will be excessive and can often result in scoring and burning of the cylinder block and valve plate bearing surfaces at the interface.

The numerous and complex forces acting on the cylinder block have been analyzed as reported for example in the paper The Thrust Balancing of Axial Piston Machines Parts 1 and 2 by N. A. Shute and D. E. Turnbull of the British Hydromechanics Research Association, identified as Research Report 772 and 773 of May and June of 1963.

The cylinder block or barrel forces include hydraulic piston thrust, hydrostatic pressure, hydrostatic and hydrodynamic bearing thrust, centrifugal couples, etc. which are supported by the hydrostatic and hydrodynamic bearing surfaces at the cylinder block and valve plate interface. Because of the variables involved, the bearing design is necessarily a compromise and the operating range of the machine is thus limited. It has been recognized that speed is a factor as the centrifugal couples and hydrodynamic bearing separating thrust both tend to vary the cylinder block balance. In applications where a small range of operating condition variations is acceptable, such a compromise cylinder block balance is sufficient. Where a larger speed range is required, it has been proposed to control the bias as a function of speed by pressurizing the hydrostatic machine housing with a pressure proportional to speed. In accordance with this invention, we propose a hydrostatic machine having an improved biasing control motor and biasing control system providing improved efficiency and a wider range of operation. This biasing control system employs a biasing motor connected between a member of the hydrostatic machine axially fixed to the transmission housing and the axially movable cylinder block or barrel. The motor has a pair of end walls, one axially abutting the member and the other axially abutting the cylinder block and providing a chamber between the end walls and the cylindrical surfaces on the member and the cylinder block and provides in response to fluid pressure in the chamber a biasing force on the cylinder block to urge it into engagement with the valve plate. In one arrangement, the axially fixed member is a sleeve portion of the housing extending within a bore in the cylinder block or barrel with annular end walls therebetween rotatably fixed to the member to which it is axially secured or rotating at an intermediate speed to reduce seal speed. The end walls are close together so a minimal area of the cylindrical surfaces is contacted by the fluid. This motor also functions as a fluid transfer seal between the fixed sleeve and cylinder block. In another modification, the axially fixed member is the shaft extending through the cylinder bore and since there is no relative rotation, the seals merely move axially on the shaft and in the bore.

Fluid pressure controlled by a speed governor is supplied to the biasing motor to provide a bias proportional to speed. In one arrangement a two step upstream type governor is employed. In another arrangement a single element upstream governor is employed. These governors are mounted in the cylinder block between the cylinders and only require a single orificed feed connected to the biasing motor and speed governor valve. In another modification, the fluid pressure supplied to the biasing motor chamber is controlledby speed, the differential power system pressure and displacement. The control provides a biasing force increasing with increasing speed, decreasing with increasing system pressure and increasing with increasing displacement for maximum efficiency improvement. While in the general application of such a control to hydrostatic machines the effect of speed is more significant, it will be appreciated that applications having a small speed range and a larger differential pressure or displacement variation range could employ such controls having a biasing control responsive to differential power system pressure or displacement variation or both with or without the speed control. With such a balancing system providing a supplementary cylinder block bias varying as a function of speed, differential system pressure or displacement or a combination thereof, the basic cylinder block thrust forces may be balanced to meet the minimum or less than minimum needs with respect to the speed range, differential pressure range and/or displacement variation range rather than the conventional practice of balancing for average or severe conditions. The bias control pressure provides a supplementary cylinder block bias which when added to the basic thrust forces provides a total thrust force bias meeting the requirements for optimum performance, minimum leakage with minimum friction, throughout variations in a large operating range of speed, differential pressure and displacement.

In the axial pumps of the type shown, the supplemental bias requirements increase with increasing speed substantially as a function of speed. Thus governor pressure acts on the bias pressure regulator valve to increase bias pressure as a function of speed signal pressure. This increase of bias requirements with increasing speed is however reducedand finally eliminated with increasing hydrostatic system pressure and thus system pressure opposes the speed signal acting on the bias regulator valve to reduce and then eliminate the bias pressure increase due to speed. Thus at high system pressures the speed effect is removed. Bias requirements also increase with displacement independently of the above functions so a displacement signal pressure proportional to displacement increases the bias pressure proportional to displacement independently of speed and hydrostatic system pressure.

The displacement control follow-up valve exhausts through the land bore clearance, limiting displacement rate of change. The pressure feed lubrication and dry sump improve high speed efficiency.

These and other features of the invention will be more apparent from the description and the drawing in which:

FIG. 1 is a sectional view showing an axial pump or motor hydrostatic unit with a cylinder block thrust balance control system.

FIG. 2 is a section on the line 22 of FIG. 1 showing the valve plate.

FIG. 3 is an enlarged plan view of the governor valve portion of FIG. 1.

FIG. 4 is a sectional view of a modified axial pump or motor unit and cylinder block thrust balance control system.

FIG. 5 is an enlarged partial cross section view of the governor valve of FIG. 4.

FIG. 6 is an enlarged plan view of the biasing motor of FIG. 4.

FIG. 7 is a sectional view of a modified axial pump or motor unit and biasing motor.

FIG. 8 is a schematic view of a hydrostatic pump or motor unit and a biasing control system.

FIG. 9 shows curves of biasing force or pressure for various speeds plotted against differential power system pressure.

FIG. 10 shows curves of biasing force or pressure at illustrative displacements and differential power system pressure plotted against speed.

The hydrostatic converter, a hydrostatic pump or motor unit, shown in FIG. 1, may be used as either the pump or motor in the system or hydrostatic transmission shown diagrammatically in FIG. 8. Referring to FIG. I, the hydrostatic converter has a barrel shaped housing 10, having an integral valve supporting end wall 11 at the valve end and a shaft end support wall and housing cover wall 12 at the shaft end suitably secured by bolts and sealed to close the open end of the barrel housing 10. The closure wall 12 has a central opening 14 to receive the adapter, or bushing 15, which is secured by suitable fasteners 16 to the wall 12. The shaft end wall 12 with adapter supports the shaft seal 17, rotary bearing 18, and thrust bearing 19 which rotatably and axially support and locate shaft 21 in the shaft end wall 12. The other end of shaft 21 extends into, and has rotary bearing support in the bore 22 in a cylindrical support sleeve member 23 secured and sealed, as described below with reference to FIG. 4, in opening 24 in the valve end wall 11.

On the inside face of the shaft end wall 12, there are formed, or secured, a pair of semi-cylindrical bearing members 31 and 32 having respectively the plane semicylindrical bearing surfaces 33 and 34 which extend vertically and are located on opposite sides of, and equidistant from, the axis 36 of the machine and shaft 21 and are parallel to each other. These plane semicylindrical bearing surfaces 33 on the near side and 34 on the far side of the shaft in FIG. 1 cooperate with semi-cylindrical bearing surfaces 37 and 38 respectively, on the tilt box 39. These bearings may be plain bearings or the improved hydrostatic bearings of application Ser. No. 183,959 filed Sept. 25, 1971 by Erkki A. Koivunen. The tilt box 39 is thus supported by the aforesaid semi-cylindrical bearings for rotation about a horizontal transverse axis 41 perpendicular to axis 36 and thus shown as a point in FIG. 1. The tilt box 39 is an annular member having considerable depth in an axial direction for rigidity and has a flat annular bearing surface 42. The annular wear or swash plate 43 has one annular bearing surface 44 in engagement with the bearing surface 42 on the tilt box to rotatably support the wear plate on the tilt box. The tilt box has a peripheral rib 45 having an internal cylindrical bearing surface at the perimeter interrupted at the actuator sockets, to retain the wear plate 43 in position for its rotary movement relative to the tilt box.

The other annular bearing surface 47 on the wear plate slidably supports the slippers 48 which have a foot portion 49 with a hydrostatic bearing recess 51 within a circular bearing surface engaging the annular bearing surface 47 and a ball portion 52 fitting, and suitably retained in the socket S3 of the piston 54. The piston 54 has suitable sealing grooves 56 and fits in a cylinder 57 in the rotor or rotary cylinder block 58. The block 58 contains a plurality of cylinders each having a port or opening 59 with a piston assembly in each cylinder. The illustrative embodiment has nine cylinders equally spaced about the machine axis. The block has a central opening 61 having a splined portion 62 of smaller diameter adjacent the end of the block next to the wear plate and loosely engaging splines 116 on shaft 21. A spherical bearing member 63 is suitably mounted on the shaft and biased by a plurality of coil springs 64 toward the tilt box. The spherical bearing surface has oil grooves and supports the spherical bearing portion 66 of the retainer plate 67. The retainer plate 67 has a recess 68 for each slipper fitting around the central portion of the slipper and engaging an annular surface 69 on the slipper foot to retain the slipper in contact with the wear plate by the bias of springs 64 when fluid pressure in the cylinder does not.

The tilt box 39 is rotated on the bearings 33, 34 about the axis 41 by hydraulic actuators 71 and 72 which respectively actuate the top actuator rod 73 fitting into socket 74 on the tilt box and actuator rod 76 fitting into socket 77 on the lower portion of the tilt box. The hydraulic actuators 71, 72 are identical and each has a piston 78 reciprocatable in a bore 79 and a socket 80 fitting its rod. The bore 79 has an end closure cap 82 threadably secured and sealed to the housing and having a continuation of bore 79 and a threaded port 83 to receive a fitting of a hydraulic line. A spring 84 is located in the bore and abuts the closure cap to resiliently bias the piston to engage the actuator rod in its sockets to provide a bias positioning the tilt box in the neutral or zero angle position. Suitable controls shown in FIG. 8 and described below supply actuator pressure via ports 83 to the bores 79 of the actuators 71 and 72 to position the tilt box to a desired angle. When the tilt box is in the position perpendicular to the unit axis 36 there is no pump or motor operation. The tilt box can be moved clockwise or counter-clockwise to provide, in response to the same direction of input rotation, a

pumping action in the opposite direction between the supply and return lines and motor operation in response to fluid supply in one direction to produce opposite directions of rotation.

The valve plate 86, FIGS. 1 and 2, is located between the valve end wall 11 of the housing and the rotary cylinder block 58 and has a bearing and sealing surface 87 engaging the bearing and sealing surface 88 on the wall 11 and then on the opposite side, a bearing and sealing surface 89 engaging the bearing and sealing surface 91 on the end of the cylinder block. These bearing and sealing surfaces are annular. A port 59 connects each cylinder 57 through the end of the cylinder block and its bearing surface 91. A pin 93 in the end wall 11 fits loosely in a radial slot in the valve plate 86 to prevent rotation of the valve plate 86 and permit its seating on the sealing and bearing surfaces between end wall 11 and cylinder block 58. The valve plate perimeter and shoulder 94 have bearing engagement to radially locate the valve plate in the housing. A radially inner annular groove 95 and a radially outer annular groove 96 on each opposite face of the valve plate define an annular sealing and bearing surface area or pad 97, one on each side of the valve plate. The inner grooves 95 are vented toward the center by radial groove portions in the plate or facing surfaces and the outer grooves 96 have radial portions for venting to the outer perimeter of the valve plate providing therebetween interrupted outer pad portions 98. The sealing bearing surface 87 nonrotatably engages surface 88 on wall 11 and functions as'a hydrostatic sealing bearing and may float to insure good axial alignment. While the grooves in both sealing bearing surfaces 87 and 89 divide the surface into an annular portion 97' and a plurality of radial outer pad portions 98, the sealing bearing surface 89, since it engages the rotating surface 91 on the cylinder block functions as a hydrokinetic bearing and pad portions 98 provide a greater separating effect. The ports 59 in the cylinder block 58, the ports 101 and 107 in the valve plate 86 and the main pressure ports or passages 102 and 108 in end wall 11 are within these sealing bearing surfaces to prevent exhaust or limit leakage to a low value to the interior of housing 10.

When the shaft 21 is driven in a clockwise direction,

- as viewed from the front of the unit, as indicated by the arrow A, FIGS. 1 and 2, and the tilt box is tilted as shown in FIG. 1, the cylinder block 58 rotates in this direction relative to the stationary valve plate 86 and thevalves are functional as a pump as follows. The lozenge shaped port 101 is the low pressure inlet port and is faired into an inlet or return passage 102. The initially opening end 103 of port 101 may have a tapered initial small volume slot portion. At the other side of the valve plate 86 there is the lozenge shaped high pressure port 107 which is faired into the high pressure supply line 108. At the initially opening end 109 of port 107, there may also be a shallow step portion.

The splined small diameter portion 62 of cylinder block 58 is splined to the splines 116 on the shaft 21. These splines permit a small freedom of movement between the cylinder block and shaft so the block is free to seat on the valve plate. The cylinder block move- I ment-away from the valve face is limited by the snap ring 117 but the snap ring is not normally loaded since the biasing motor device 118 normally biases the cylinder block to contact the valve plate. The biasing motor, shown in FIG. 1, has a first annular wall or piston 119 and a second annular piston 123 each having an outer diameter seal in sealing engagement with a cylindrical surface 121 on the inner diameter of the cylinder block and an inner diameter seal in sealing engagement with an outer diameter surface 122 on the support sleeve portion 23 of end wall 11. When fluid is supplied under pressure via the bias pressure passage 126 in support sleeve 23 to the space 127 between the two pistons and cylindrical surfaces 121 and 122, the piston 119 abuts snap ring 128 on the support portion 23 and piston 123 engages snap ring 129 on the inner diameter of the cylinder block, biasing the cylinder block against the valve plate with a force proportional to the fluid pressure therein. Pistons 119 and 123 may have a press fit respectively with cylindrical surfaces 122 and 121, so pistons 119 and 123 are axially and rotatably secured to the sleeve 23 and the block 58. If the pistons are free to rotate at an intermediate speed the snap rings have a sufficiently large bearing surface to accommodate relative rotation. Spacing projection 131 on the pistons, as shown in detail in FIG. 4, may be used tokeep the pistons spaced apart so the connection to the bias pressure passage 126 and passage 158 is never blocked by the pistons.

In FIG. 1,"the:motor 1 l8 acts directly between a portion 23 of end wall member 11 and the cylinder block 58 member in response to biasing pressure varying as a function of speed to provide a biasing force or pressure increasing with increasing speed between these members at the relatively rotating bearing and seal interface between valve surface 89 on valve plate or member 86 operatively fixed to end wall 11 and valve surface 91 on cylinder block 58.

The upstream regulating governor valve 135, shown in FIGS. 1 and 3, has a weight member 136 reciprocally mounted in a bore 137 radially located in the cylinder block between cylinders. The weight member has an enlarged head portion 138 which would engage in inner diameter portion 139 of the cylinder block to limit radial outward movement under certain inoperative conditions. Similarly, inward movement is limited by shaft 21. The weight transmits-centrifugal force proportional to the speed of rotation of the cylinder block through the coil spring 141 to the ball valve element 142 which, as shown, is seated against the circular seat 143 on the closure plug 144 which is suitably secured and sealed by threads 146 in the large radial outer end portion 147 of bore 137. The enlarged portion 148 of bore 137 around the ball valve element 142 permits limited movement of this valve element. This chamber, substantially at the level of the valve seat, is connected to exhaust by exhaust branch 149 to exhaust 151 which also exhausts the bore 137 between the weight and ball valve elements to the outer perimeter of the barrel. A regulated pressure source 154, i.e., the regulated supercharge-pump shown in FIG. 8, supplies a regulator control pressure, through a restriction 156 to governor bias pressure passage, external passage portion 157 and internal passage portion 126 in sleeve 23. The passage 126 is connected through space 127 to governor pressure passage 158 so the biasing motor functions as a mtor and fluid transfer device between the fixed sleeve and rotary cylinder block. Passage 158 extends through the cylinder block and cover plug 144 to chamber 159 in the cover plug beneath ball valve element 142. The upstream regulating governor valve regulates the pressure upstream thereof in space 127 and lines 158,

126 and 157 to orifice 156 at a pressure proportional to speed by exhausting fluid to exhausts 149, 151 to reduce excess pressure. This exhaust from the governor valve and all other exhaust and leakage, as from the valve interface, pistons and cylinders and hydrostatic bearings drains within housing 10 to sump portion 152 which is exhausted to maintain a dry housing by gravity or suction drain 153 and returned to the sump of regulated pressure source 154. The upstream governor pressure line 157 may be connected by restriction 161 and governor pressure'passage 162 to supply a pressure varying as a function of speed to other control devices for controlling the hydrostatic or gear transmission components. Restriction 161 is smaller than restriction 156 to limit flow to a lower value than the supply flow through restriction 156 so there is excess fluid for governor valve regulation. The normal low flow control system provides such limited flow. Governor valve 135 is located between cylinders like governor valve 185, FIG. 5, described below.

MODIFIED BIAS CONTROL The modified hydrostatic unit and biasing control system shown in FIG. 4 has a similar transmission housing 10' with an end wall 11' and a closure wall 12' rotatably supporting a shaft 21' on which the cylinder block 58' is rotatably mounted in engagement with the valve plate 86'. The pistons 54 are reciprocated by the swash plate structure 39' pivotally mounted in the bearing members 31 and 32' on the cover and the displacement is controlled by the displacement control motors 71' and 72'. These assemblies and their elements in FIG. 4 are the same as those described above with reference to these unprimed reference numerals in FIG. 1 and are indicated by the same reference numerals primed in FIG. 4 and for a description refer to the above description of FIG. 1 except for the following features of the FIG. 4 modified bias control system.

In the FIG. 4 modification, the biasing motor acts directly between shaft 21 and cylinder block 58 and thus support sleeve member 23' is modified and terminates at end 165 in the same plane as surface 88 on end wall 11' and has internal bearing 166 supporting shaft 21 and a modified passage and transfer device described below. The valve plate 86' is the same except the inner diameter is smaller.

As in FIG. 1, in FIG. 4, the cylinder block 58 has a splined portion 62' splined to the splines 116' on the shaft 21 'to permitting a small axial movement between the cylinder block and shaft so the block is free to seat at a controlled pressure on the valve plate. The biasing motor 167, shown in FIGS. 4 and 6, has a first annular wall or piston 168 and a second annular wall or piston 169, each having respectively outer diameter seals 170 and 171 sealing with a cylindrical surface 172 on the inner diameter of the cylinder block and inner diameter seals 173, 174 sealing with an outer diameter surface 175 on the shaft 21'. When fluid is supplied under pressure via the inlet passage 176 in shaft 21, to the space 177 between the cylindrical surfaces and two pistons, the piston 168 abuts shoulder 178 on the shaft and the diagonally opposite edge of piston 169 enages snap ring 179 seated in a groove in the cylinder block nearer the valve interface than shoulder 178, biasing the cylinder block against the valve plate with a force proportional to the fluid pressure therein. There is always clearance 166 and 184 at the other diagonally opposite edges. At

the outer diameter of the pistons 168, 169, each has an interrupted annular ring projection 180 and 181 respectively which have a plurality of radial recesses 182 at the facing surfaces thereof to prevent sealing which keep the pistons spaced apart so the connection to and between the inlet passage 176, and governor feed passage 183, is never blocked by the pistons. The governor feed passage 183 extends radially through the cylinder block between cylinders 57 to the governor valve 185.

The governor valve 185, FIG. 5, has a movable valve element 187 having a stem 188 reciprocably mounted in valve sealing relation in the bore or passage 183 and a head portion 189 cooperating with the sealing edge or seat 191 on a fixed seat member 192 positioned in an enlarged bore portion 193 of the bore 183 with sufficient clearance and longitudinal grooves to provide an exhaust passage 194 between seat member 192 and bore portion 193 to a cross slot passage 195. The seat member is retained therein by snap ring 196 but the clearance permits lateral movement in the bore for seating alignment with the valve head 189. The fluid supplied under pressure in passage 183 communicates through a central passage 197 in the valve element 187 to the chamber 198 between the valve element head 189 and the seat member 192. When the pressure in chamber 198 overcomes centrifugal force acting on the valve element 187 to open the valve, the fluid is permitted to flow to the exhaust space 199 and communicates through the clearance and/or passage 194 and cross slot passage 195 to space 201 between the cylinder block 58' and housing 10 from which it drains to sump portion 152 and is evacuated through exhaust passage 153. The fluid level in the sump is kept low so the fluid does not contact the rotating cylinder block or other rotating parts. All leakage fluid is drained to the sump 152 as by drain passages 202 which drain control fluid leakage and lubricating fluid to sump 152'. The internal sump 152 by exhaust passage 153 is connected to an external sump 203 or to suction of the engine driven pump 204. The engine driven pump, at a pressure'regulated by the regulator valve 205, supplies fluid under pressure to the supply passage 206 which communicates via the transfer sleeve passage 207 through the restriction 208 in line 176. A control system and supercharge pressure of about l psi is used. The transfer passagesleeve 207 conveys fluid from the fixed housing to the passage 176 in the rotary shaft which supplies fluid under pressure to the space between the pistons 168, 169.

The governor valve regulates the pressure upstream of the valve to the restriction 208 at a governor pressure proportional to the speed of rotation of the cylinder block relative to the housing. The restriction limits flow to, and exhaust from, the governor valve so there is constant governor pressure in the passages between the restriction 208 and governor valve 185 to act on pistons 168, 169 to bias the cylinder block against the valve plate with a force proportional to speed. This is an auxiliary biasing device to augment the built-in cylinder block balance to prevent cylinder block lift-off at high speeds to extend the high speed operating range of the hydrostatic machine. The cylinder block is'biased toward the valve plate by power system fluid pressure in the cylinders acting on the difference between cylinder area and the area of ports or openings 59 and counter balanced by the hydrostatic and hydro-kinetic sealing and bearing forces occurring between the valve plate surfaces and the adjacent surfaces on the end wall and cylinder block called the valve interface. This balance diminishes with increasing speed due to increasing hydrokinetic bearing forces and is augmented by governor pressure on pistons 168, 169 to prevent incipient lift-off which increases leakage and reduces efficiency and, of course, full lift-off, a more serious condition causing substantial leakage, loss of power and noise.

MODIFIED I-IYDROSTATIC UNIT BIAS SYSTEM A modified biasing control system on a hydrostatic unit having a driven trunion mounted swash plate is shown in FIG. 7. This hydrostatic unit has a fixed housing 211 having an integral cylindrical portion 212 and an end wall portion 213 and an attachable cup-shaped cover portion 214 suitablysecured to the cylindrical portion by suitable fasteners, the lugs and bolts 215. The end wall 213 has a central aperture 216 receiving the sleeve member 217 and a cover plate 218, both secured to theend wall by bolts 220. The sleeve member and cover plate secure and fasten the bearing 219 and seal 221 whichrotatably support, axially locate and seal the shaft 222 with respect to the housing. Sleeve v 217 has a portion 223 projecting within the cylindrical portion 212 of the housing in which the antifriction bearing 224 is secured to rotatably support the mid portion of shaft 222 immediately adjacent the head portion 225 of the shaft. The enlarged head portion 225 has drive splines 226 on the outer diameter meshing with splines 227 on the inner diameter of the cylinder block 228. The cylinder block has a valve surface 229 perpendicular to the shaft axis 251 in engagement with the face 231 of valve plate 232. Valve plate has a valve surface 233 in face engagement with the valve surface 234 on the end wall 213. The valve plate 232 seats on the end wall with a hydrostatic bearing at the interface 233, 234 and the valve plate is prevented from relative rotation with the wall 213 by the pin and slot fastener 236 which permits limited relative movement for full surface seating. The valve plate has annular and radial grooves, like the above described valve plate 86, at the hydrostatic bearing and interface 233, 234 and at the hydrostatic hydrokinetic bearing interface 229, 231 which function in a similar manner. The cylinder block 228 has an annular series of cylinders 237 each connected by port opening 238 to the interface 229, 231. Valve plate 232 has a pair of oppositely disposed lozenge shaped ports like the above described valve plate 86, FlG. 2, each port, one port 239 being shown, is connected at all times to the high and low pressure port passages in the end wall 213, one passage 24] being shown. The port 239 and passage 241 are shown in this section to illustrate a connecting position but this port and passage are on one side and the other port and passage not shown are on the opposite side of this otherwise vertical section as shown in FIGS. 1 and 2. A piston 242 is reciprocally mounted in each cylinder 237 and each piston has a ball socket 243 to receive the ball end 244 of the piston rod 245. The tilt box 246 has trunions 247, one projecting from each opposite side thereof and rotatably mounted in the bearings 248 one in each opposite side portion 249 of housing cover portion 214 to rotatably mount the tilt box 246 for limited tilting movement about the transverse axis 250, a

point in FIG. 7, which passes through the machine or shaft axis 251, a dot-dash line in FIG. 7, at the center of the universal drive joint 252 described below. The annular drive plate 253 is rotatably mounted on the tilt box by the annular roller thrust bearing 254 and rotary bearing 255 which may be anti-friction bearings as shown in the A. F. Anderson Pat. 3,186,352 issued June 1, 1965. The drive plate 253 has a socket to receive the ball end 256 of each'piston rod 245.

The shaft 222 is connected to drive the drive plate 253 by the universal drive assembly 257 which includes a shaft 258 having integrally formed therewith at the input end universal joint ball 259 of the universal joint 252 which fits within the'head 225 and at the output end the universal joint ball 260 which fits within the universal joint-socket 261 forming the universal joint 262.

Lubrication passage 263 in the wall 213, passage 264 in the shaft 222 and passage 265 in the universal joint drive assembly 257 supply lubrication to the shaft bearings, universal joint drive assembly and drive plate bearings further described below. Displacement is varied by a pair of actuators or motors 266, 267 like the motor described in FIGS. 1 and 4. The motor 267, shown at the bottom of the FIG. 7, has a piston 268 reciprocally mounted in a cylinder 269 and biased by a spring 271. Control fluid is supplied by port 272. The piston 268 and tilt box 226 are interconnected by a rod 273 pivotally connected to each of these members. The particular motor control system for tilting the tilt box 246 and the details of the ball joints may also be constructed in accordance with the aforesaid patent 3,186,352. The opening 274 drains the housing and is connected to a sump. 1

The variable biasing motor 276 has a first annular piston 277 having external diameter and internal diameter seals respectively in contact with the internal diameter cylindrical surface 278 on the cylinder block 228 and the external diameter cylindrical surface 279 on shaft 222. The second annular piston 28] has external and internal seals respectively in sliding engagement with the cylindrical surface 278 of the block and a second internal cylindrical surface 282 on the head portion of shaft 222. Thus there is a sealed annular space 283 between the pistons and'cylindrical surfaces on the shaft and cylinder block which is connected by a passage 284 in sleeve portion 223 to the passage 285 in the end wall 213 which terminates at the port 286. Governor or biasing pressure is supplied to this port to control the biasing force provided by the biasing motor 276. Since the shaft 222 is axially fixed to the housing, the biasing motor which has a pressure chamber between a second piston 281 engaging the shaft shoulder 287 and a first piston 277 engaging shoulder 288 on the cylinder block, the motor will, proportional to fluid pressure in the chamber, bias the cylinder block to con- -trol the contact pressure at the hydrodynamic, hydrokinetic valve interface 229, 231. The first piston 277 is secured against rotation and axial movement relative to block 228 respectively by a press fit or tighter seal in cylindrical surface 278 and shoulder 288 and free relative to shaft 222. The second piston 281 is similarly secured against rotary and axial movement relative to shaft 222 and free relative to block 228. A clearance between the first piston 277 and the sleeve portion 223 and the shaft head permits the required axial movement.

The lubrication system has a fluid supply system having a sump, pump and regulator valve as shown in FIG.

1 supplying fluid under pressure to lubrication line 263. The lubrication line 263 and biasing pressure line 285 are adjacent each other in wall 213 and continue through sleeve 217 and fluid transfer bushing 289 which is fixed within sleeve 217 by a suitable pin fasterier. Lubrication passage 264 and bias pressure passage 284 each connect to an annular groove in the outer diameter of shaft 222 having a seal on each side of and between the grooves. The grooves are aligned respectively with passages 263 and 285. Passage 263 in transfer bushing 289 is connected by restricted passage 219' to supply fluid to bearing 219 for lubrication and also supply fluid from the space between sleeve 217 and shaft 222 adjacent bearing 219 through restricted passage 224 to bearing 224 for lubrication. Passage 264, which includes the annular groove connected to passage 263, connects to a bore 222' in shaft 222. A

spring 290 seated in bore 222 axially biases the seal member 290' which is sealed in bore 222 so its spherical face sealingly engages the spherical face of seal member 259 and seals it to the end face of shaft 258 to provide a fluid connection of passage 264 through bore 222', passage 265 in both seal members to passage265 in shaft 258 to maintain the pressure connection regardless of tilt box position. The seal member 259' has a portion loosely fitting in passage 265 to permit limited transverse centering movement. The flat annular interface between the end of shaft 258 and seal member 259' has radial grooves 258' which may be entirely in the shaft as shown for lubrication of the interface and ball joint 259, entirely or jointly with passages 252'. Seal member 290' has radial restricted passages 252' connecting passage 265' to lubricate ball joint 252. Restricted passages 262' connect passage 265 to lubricate joint 262. At the ball 260 end passage 265 has a seal member 260' also loosely fitting in passage 265 for centering. The seal member 260' is held in position by the ball guide retainer seal member 261' which seals the outboard end of joint 262 and has a spherical portion engaging the spherical side of the seal member 260 lubricated by restricted passage 263'. Radial grooves in the flat annular interface between the seal member 260 and the adjacent end of shaft 258, as shown by grooves 254' in the shaft end connect passage 265 to supply lubrication to the interface and the ball joint 260. The seal member 260 and retainer seal member 261 thus close the end of passage 265 except for flow to the ball joint 260 and enclose the outboard end of the ball joint. Restricted radial passages 262' may also directly connect passage 265 to lubricate ball joint 260. The hub portion of drive plate 253 has radial restricted passages 254' radially aligned with roller bearing 254 to centrifugally throw fluid to lubricate bearings 254 and 255. The restricted passage 254' permits less flow than passages 254 and 262 to retain fluid in, and lubricate, ball joint 260. All leakage fluid from the pump pressure, control and lubrication systems is drained via drain port 274 to a sump or pump suction to maintain a dry housing.

MODIFIED HYDROSTATIC TRANSMISSION AND BIAS SYSTEM The hydrostatic transmission, FIG. 8, has a pump 291 and a motor 292 interconnected by hydrostatic power circuit pressure lines 293 and 294 which transmit the high and low pressure hydrostatic fluid between the pump and motor to provide the operating phase described below. The pump and motors normally have an identical structure and may be like the above described pumps with a pump essentially like the pump of FIG. 4 being illustrated. The motor has an output shaft 295. The pump 291 has a fixed housing 296, which has suitable bearings, as shown in FIG. 4, to rotatably support the input shaft 297 for drive by the engine in the direction of arrow E. Cylinder block 298 has suitable internal splines and the shaft 297 has external splines to provide the spline drive 299 which permits relative axial movement and tilting or coupling movement so the valve surface or face 301 engages and seats on the valve face 302 on the valve plate 303 which like above valve plate 86 is attached to the housing end wall 304 or may be integral with the housing end wall. The cylinder block 298 has an annular series of cylinders 306 each having a port opening 307 extending to cylinder block valve face 301 and alternately connected to the lozenge shaped ports 308 and 309 in the valve plate which are respectively continuously connected to passages 293 and 294. These valve plate ports and the passages are shown in a transverse plane. When the shaft is driven clockwise as viewed from its input end, arrow E, and the tilt box is in a forward angle as shown, high pressure fluid is supplied to port 308 and passage 293 which are on the far side of the axis, as port 107, FIG. 2, and low pressure fluid is received from suction or inlet port 309 and passage 294 on the near side of the axis, as port 101 FIG. 2. This forward drive flow is indicated by arrows FP. Each piston 311 is pivotally connected to a slipper 312 which slidably engages the bearing surface 313 on the tilt box 314. The tilt box 314 has a trunion 316 at each side pivotally mounted in the side housing portion 317 to permit tilting of the tilt box through the forward displacement angle f and the reverse displacement angle r. The piston reaction forces tend to move the tilt box to the neutral position N. Variable displacement control actuators or motors 318 and 319 vary the forward and reverse tilt box and thus vary displacement. The reverse control motor 318, at the top of the Figure is so called because reverse displacement is increased when a higher pressure is supplied to this motor. The forward motor 319, at the lower part of the Figure, is so called because forward displacement is increased when a higher pressure is supplied to this motor. Each motor has an axially extending cylinder 321 with a piston 322 reciprocally mounted therein and connected by a piston rod 323 pivotally connected at one end to the piston and at the other end to the tilt box. A coil spring 324 is located in each cylinder and engages the piston and the end of the cylinder at the control pressure port 325 to bias the pistons and the tilt box to neutral position.

The control system has a reservoir or sump 331 from which fluid is supplied by the pump inlet line 332 to the input shaft driven supercharge pump and regulator 333 which supplies fluid at a regulated pressure, i.e., psi, to the main line 334. Main line branch 335 supplies makeup supercharge pressure respectively through one-way valved branch passages 336 or 337 permitting flow only from main line to the one of the lines 293 or 294 which is under suction or lower pressure (less than 100 psi) and under the higher (above 100 psi) pressure in the other line blocking flow to the high pressure line. The main line branch 338 supplies fluid under pressure to the governor 339 which provides a speed governor signal pressure proportional to shaft speed in the speed signal pressure line 341. This governor may be a conventional transmission governor or the governors of FIGS. 1 and 4.

The displacement control valve 342, a follow-up type valve, has a valve sleeve element 343 located in a valve bore 344 in the valve body 345, a spool valve element 346 having lands a and b of equal diameter is located in the bore 347 of the sleeve 343. The sleeve has an end wall 348 providing a seat for spring 349 positioned between the end wall and land b of valve spool 346. The valve sleeve 343 has an car 351 pivotally connected to a link 354 which is also pivotally connected to control lever 352 to move the valve sleeve 343 in accordance with movement of the control lever 352. The manually operated control lever 352 is pivotally mounted by pivot 353 on a fixed portion of the control body housing and is movable from a central neutral position N in one direction through increasing forward displacement positions to a full displacement forward position F and in the opposite direction through increasing reverse displacement positions to a full displacement reverse position R and similarly positions the valve sleeve.

Spool valve element 346 is moved in accordance with displacement by a cam follower rod 356 guided for reciprocal movement in a housing guide portion 357 and having one end engaging a seat 358 in the end of the valve element opposite spring 349 and the other rod end engaging cam 359 fixed on and movable with the tilt box 314 to move the valve element 346 in accordance with displacement of the pump unit 291. 1

The hydrostatic system pressure lines 293 and 294 are respectively connected to one-way valve passages 361 and 362 permitting flow only from the system pressure line having higher pressure to the high system pressure passage 363 and blocking flow to and from the other system pressure line having lower pressure. The system pressure passage is connected to the central port 364 of the displacement control valve 342. The upper or reverse port 366 is connected to the reverse control pressure passage 367 and reverse control motor 318. The lower or forward port 368 is connected to the forward control pressure passage 369 and forward control motor 319. The valve sleeve 343 has a central port 371, a reverse port 372 and a forward port 373, each having an annular external recess in the outer diameter of the sleeve and being connected through the sleeve by apertures to an internal port opening. The external recesses of ports 371, 372 and 373 in the sleeve are connected respectively to ports 364, 366 and 367, in the valve body in all positions of the sleeve relative to the valve body. The internal port opening of central port 371 is always'connected to the space between lands a and b of spool valve 346. The distance between the port openings of reverse and forward ports 372 and 373 is the same or slightly larger than the distance between lands a and b so in neutral position, with tolerance latitude, the flow of high system pressure from line 363 to both displacement control passages 367 and 369 is blocked. The lands a and b of spool valve 346 have a small normal clearance in sleeve bore 347 which is sufficient to provide a damped controlled rate of change of displacement readily controlled by clearance and land length. Exhaust 374 in sleeve end wall 348 freely vents this leakage exhaust across land b and the other end of the sleeve is open to freely vent leakage exhaust across land a.

A bias control valve 378 has a regulator valve element 379 having equal diameter lands a and b in the large bore portion 381 and a smaller diameter land c in the small bore portion 382 and-reciprocates in the stepped bore 381, 382. The end of bore 381 adjacent land a is closed by the fixed plug 383. The internal passage 384 in valve element 379 connects the space between the lands a and b to the closed chamber end of the valve element beyond land a. The valve bore below portion 382 has an enlarged spring chamber spring portion 386 and a further enlarged end bore portion 387 which receives the spring seat and sleeve member 388. A spring 389 is seated on a transverse wall portion 391 of member 388 and engages a spring seat 392 fixed on the lower end of valve element 379. A valve piston element 393 is reciprocally mounted in the bore 394 of the spring seat and sleeve member 388 and has a stern portion 395 extending in sealing relationship through opening 396 in wall 391. A bore closure plug 397 is fixed in the lower end of bore 387 and secures the spring seat sleeve member 388 in position and seals the lower end of its bore. The governor pressure line 341 is connected to the lower end of bore 394 to act on the full area of piston 393 to provide a valve force in the same direction as the spring 389. The high hydrostatic system pressure line 363 has a branch 398 connected to the upper end of bore 394 to act on the small area of the valve piston 393 around stem 395 opposing the governor force. The spring chamber within bore portion 386 is vented by exhaust 401. The forward and reverse displacement control lines 367 and 369 are respectively connected by the one-way valved branches 402 and 403 which only permit flow from the displacement control line having the higher pressure to the displacement signal line 404 connected to the large bore portion 381 at the step with the small bore portion 382 to act between lands b and c of valve element 379 and thus on the differential area of land b in a pressure increasing direction with the spring 389. The main line branch 406 is connected to the bore 381 at the control edge of land a for control by this edge of land a. The bias pressure line 407 is connected to the bore about midway between the facing control edges of land a and b so it is always open between the lands a and b. Exhaust 408 is connected to bore 381 for control by the control edge of land b. The bias pressure line 407 is connected by a transfer bushing 409 to a passage portion 411 in shaft 297 which is connected to the space between the pistons of bias motor 412 constructed as described above, FIGS. 1 and 4. The housing drains 414 are connected by drain line 415 to return leakage fluid to the sump to maintain a dry housing.

The FIG. 8 transmission in the forward drive operating phase with the pump shaft driven in the direction of arrow B and the tilt box 314 in a forward drive displacement angle, as shown, delivers hydrostatic system high pressure fluid to the system line 293 which flows as indicated by the arrow FP to the motor 292 to drive its output shaft 295. The motor exhaust fluid is conveyed by the low pressure return line 294 to the pump inlet or suction port 309 as indicated by the arrow F8. The supercharge pump and regulator supplies regulated main line pressure which, via branch 335 and one-way check valve 337, supplies makeup and supercharge pressure to the low pressure power system line 294. The high pressure power system line 293 is connected by the one-way valve 361 to the high power system pressure line 363 to provide the high power system pressure signal. Main line pressure is also connected to the governor 339 which, during rotation of shaft 297,

provides a speed signal pressure in governor signal line 341.

In order to maintain the pump 291 in the'full displacement position shown, the displacement control valve 342 is in displacement maintaining condition regarding the relative position of the sleeve 343 and the spool 346. In this position the spool is slightly out of the central position with respect to the sleeve so that the land a very slightly closes the opening of port 372 and the land b slightly opens the openings of port 373 so that enough pressure is supplied to the forward pressure control line 369 to supply motor 319 with sufficient pressure to overcome the reaction forces in the tilt box 314 to hold them in the full displacement position and to make up for the slightly higher leakage in the motor 319 due to the higher pressure therein as compared to motor 318. This condition, to a reduced degree, will also exist in other intermediate displacement positions. When it is desired to reduce displacement, the lever 352 is moved from the F position toward the N position, initially causing the sleeve 343 to move relative to the spool to provide a partial or full connection from the system pressure line 363 through ports 364 and 371 to the space between the lands and then to ports 372, 366 and line 367 which will supply fluid pressure to motor 318 to reduce displacement. Fluid pressure must be exhausted from motor 319 through line 369, port 368 and through the clearance space around land b and across land b. This occurs at a controlled predetermined rate to control the rate of decreasing displacement.

As the pressure in motor 318 reduces displacement, the tilt box rotates and rotates cam 359 pushing on rod 356 to move the valve spool 346 against spring 349 in a closing direction to close the valve or return the valve to its maintaining condition when the tilt box reaches the lower angle called for by the position of the displacement control lever 352 to terminate control movement and maintain the desired displacement position.

In a similar manner, when the control lever 353 is moved from neutral or a low displacement position to a higher displacement position, sleeve 343 moves with respect to the spool valve 346 to first connect the system pressure port 364 between the valve spool lands to the ports 373, 368 and line 369 to motor 319 to increase displacement. As the displacement increases the tilt box through the cam 359 and cam rod 356 permits the spring 349 to move the valve spool in a closing direction and when the displacement condition called for by the position of the control lever 352 and valve sleeve 343 is reached, the valve will be in the maintaining condition and maintain such displacement position. Since the valve spool 346 has a clearance in the sleeve bore 347 there is a restricted supply flow from inner supply port 371 to inner supply ports 372, 373 which is less restricted than the exhaust flow to pressurize both motors. Movement of the tilt box 314 or swash plate moves the spool valve relative to the sleeve to radidly decrease the supply restriction and slightly increase the exhaust restriction of one motor and increase the supply restriction and decrease the exhaust restriction of the other motor to move the tilt box in the opposite direction. Thus each maintaining coinciding position is an auto regulating position, regulating equal pressures in the motors for neutral and increasing pressure in motor 319 for increasing forward displacement and increasing pressure in motor 318 for increasing reverse displacement and responsive to tilt box drift from any position to so control flow to and exhaust from the motors to counteract the drift for auto regulation of displacement at any controlled sleeve member position. Positioning the displacement control lever 352 in reverse positions between N and R similarly positions the tilt box 314 in reverse angle r which reverses the direction of the pumping action and supplies high pressure fluid from the pump to the motor via system line 294 and then the line 293 acts as a return line returning the fluid at low pressure to the pumps intake. During vehicle overrun, the displacement control will be operated in the forward quadrant since the motor 292 on overrun acting as a pump supplies high pressure fluid via line 294 in the direction of the arrow FS to the pump 291 which now acts as a motor and returns fluid at low pressure in the direction of arrow FP through line 293 to the motor 292. t

The pump 291 having been designed to meet minimal or less than minimal bias requirements as compared to being designed to meet average or maximum required balance requirements relative to the thrust, system pressure, hydrostatic and hydrokinetic bearing, coupling etc. forces determining bias requirements of the cylinder block against the valve plate at their interface 301, 302 is provided with a bias control system to provide a bias varying as a function of pump speed, system pressure and displacement angle. The bias pressure control or regulator valve 378 receives main line pressure from branch 406 of main line 334. The bias control pressure in line 407 is always connected between the lands a and b of valve element 379 and via passage 384 to the closed end of the bore to act on the free end of land a. If this biasing pressure is above the requirements determined by the biasing pressure controls acting on this valve, the valve element 379 moves so land a closes or more nearly closes the supply pressure line 406 and land b partially or fully opens exhaust 408 to exhaust and reduce biasing pressure in line 407. If the bias control signal in line 407 requires increased pressure, valve element 379 moves so land b closes or more nearly closes exhaust 408 and opens or increases the opening of the port of line 406 to supply more fluid to biasing signal line 407. The spring 389 acts on the valve element 379 with a force providing a basic level of bias pressure in line 407. The governor signal pressure from line 341 acts on the piston 393 which, through stem 395, engages regulator valve element 379 to increase the bias signal pressure as a function of increasing pump speed. The high hydrostatic system pressure via branch line 398 acts on the small area of piston 393 opposing and reducing the effect of governor pressure acting to increase the biasing pressure with increasing speed and thus reduces biasing pressure with increasing system pressure. The pump operating forces acting on the tilt box are balanced to maintain and overcome to change tilt box position by the spring and hydraulic forces provided by the displacement control motors 318, 319. The springs in the motors provide a force inversely proportional to their elongation so that, in forward drive, as shown in FIG. 8, the spring of motor 318 is providing a larger force than the spring of motor 319. Thus to maintain a forward displacement position the pressure in line 369 must be substantially larger than the pressure in passage 367 and this displacement control pressure in line 369 varies as a function of the degree of displacement from neutral during forward displacement control. The displacement control pressure in 'line 367 similarly varies as a function of displacement during, reverse displacement operation. The higher of these two pressures, which is the effective displacement control pressure varying as a function of forward or reverse displacement from neutral, is selectively connected by the check one-way valved passages 402, 403 to the displacement control signal line 404 and acts on the unbalanced area of lands b and c of the bias control valve to increase the bias pressure as a function of increasing displacement in either a forward or a reverse direction.

A typical example of the required supplemental bias for optimum efficiency through a wide range of speed, hydrostatic system pressure and displacement for a typical axial piston pump of the type disclosed herein is shown in FIGS. 9 and 10. In FIG. 9 there is plotted on the axis of ordinates the required supplemental cylinder block hold down or bias force for optimum efficiency and on the axis of abscissas the differential pressure AP. In these charts, we have used differential pressure, the difference between the high pressure and the low or suction pressure of the hydrostatic pump or motor unit, in order to provide a pressure value representing the pressure provided by the pump or the pressure available for conversion to work in a motor. This, of course, still makes thecurves illustrative for hydrostatic units which are not supercharged or which are supercharged to varying degrees since the differential pressure eliminates the supercharge pressure value. As

shown in FIG. 9, by the family of curves, the required hold down force diminishes with increasing differential pressure at each speed value. It appears with regard to .the units we investigated that this decreasing relationcific hydrostatic hydrokinetic bearing design and theproportionalrelationship of these effects produced by each specific design will effect variations in these relationships along the lines indicated by these curves. The set of curves, each at a different speed, e.g., from 2,500 rpm to 4,000 rpm illustrates the typical variation of the hold down force with increasing speed. This again shows an essentially straight line relationship but due to the increasing hydrokinetic effects at higher speed, there would appear to be some slight increase on a square type curve particularly in the high end of the speed'range where the hydrokinetic effect is more dominant than the hydrostatic effect. In FIG. 10, the same hold down force is plotted on the ordinate and input speed on the abscissa. The set of curves shown in solid lines are all plotted at a constant differential pressure of 400 psi. The respective curves, as indicated by the legends, are 0.4, 0.6, 0.8 of full displacement and 1.0 of full displacement. This family of curves illustrates that at any constant differential pressure and any selected input speed, the required hold down force varies as a function of displacement requiring increased hold down force with increased displacement at a selected speed. These curves also show that increased hold down force is required with increasing speed, at

. selected differential pressure and displacement. The

second family of curves for a differential pressure of 650 psi. similarly illustrates these relationships as indi cated by the legend for each curve of this family. The relationship between the family of curves for a differential pressure of 400 psi are shown in solid lines and the family of curves for a differential pressure of 650 psi also indicates that the relationship is dependent on differential pressure, showing that the required hold down force decreases as a function of increasing differential pressure.

In this specification, reference to the location or position of certain parts as upper or lower, etc. relative to their position in the drawing, has been made only for convenience in referring to the drawing in conjunction with the specification and are thus merely descriptive of the illustrated preferred arrangements. The specific position of hydrostatic pump and motor units and their components, as is well known in the art, is generally subject to variation and the units may be employed or operated in any position and the components only require the above described relative arrangement for accomplishing the described functions.

It will be appreciated that other equivalent embodiments of the several disclosed embodiments or modifications may be made.

It is claimed: a

1. In a hydrostatic pump or motor unit; a housing; cylinder barrel means rotatably mounted in said housing for rotation about an axis and axially movable mounted for limited axial and transverse seating movement; a first transverse valve surface on said housing having a first and a second port for high and low pressure; a second transverse valve surface on said barrel means in continuous rotary surface seating engagement with said first surface providing an interface seal; a plurality of cylinders in said barrel means each having a third port connected to said second surface and alternately being connected to said first and second ports and said ports being sealed by said interface seal during rotation of said barrel means; pistons in said cylinders;

means to reciprocate said pistons in said cylinders; bias motor means having an axially fixed member with an external concentric cylindrical wall axially fixed relative to said housing and an internal concentric cylindrical wall on said barrel means and two axially short annular piston members each having inner and outer diameter seals in contact respectively with said external and internal concentric cylindrical surfaces, one piston member being adjacent said interface seal, and freely slidable on said external cylindrical wall; the other'piston member being remote from said interface seal and freely slidable on said internal cylindrical wall; means on said barrel means to limit axial movement of the annular piston member adjacent said interface seal relative to said barrel means toward said interface seal and means on said axially fixed member to limit axial movement of the other annular piston member remote from said interface seal relativeto said axially fixed member away from said interface seal and said annular piston members being closely axially spaced to provide an axially short expansible chamber for fluid having minimal fluid contact with said concentric cylindrical walls responsive to fluid pressure in said chamber to bias said barrel means for axial movement against said housing for pressure engagement of said interface seal permitting seating movement and control means to supply a bias control pressure to said chamber of said bias motor means.

2. The invention defined in claim 1 and said axially fixed member with an external cylindrical surface being a sleeve fixed to said housing and projecting in spaced relation into said external cylindrical surface providing said concentric cylindrical surfaces.

3. The invention defined in claim 1 and said axially fixed member with an external cylindrical wall being a shaft of said barrel means rotatably mounted and axially fixed relative to said housing and said barrel means including a barrel member secured to said shaft to rotate with said shaft and to permit relative axial and transverse seating movement.

4. In a hydrostatic pump or motor unit; a housing; a port member having a first valve surface; a high pressure port and a low pressure port in said first valve surface; a cylinder member having a cylinder, a second valve surface in matching surface sealing contact at the interface with said first valve surface and an opening in said second valve surface to said cylinder; support and bearing means mounting said port member and said cylinder member in said housing for relative rotary and axial movement of said port member and said cylinder member toward each other for varying pressure continuous sealing engagement of said valve surfaces to control interface leakage and said opening being alternately connecting with said high and low pressure ports during said relative rotation of said members; a piston in said cylinder; reciprocating means operably connected to said piston and said members for reciprocating said piston in said cylinder responsive to said relative rotation of said members; closed expansible chamber fluid bias motor means having relatively movable parts moved by fluid under pressure, one part operatively connected to said port member and the other part operatively connected to said cylinder member and operated by fluid bias pressure supplied to said closed expansible chamber to bias said valve surfaces of said members into sealing engagement; said housing enclosing the assembly of said piston, said cylinder member and said port member and collecting leakage fluid from said assembly; drain means operative to drain said leakage from said housing to provide a dry housing; a signal means providing a signal varying as a function of a condition of operation of the unit varying with said interface leakage and control means operatively connected to said bias motor means and said signal means to supply a bias fluid pressure in said bias motor means varying as a function of said condition of operation to control the bias force between said valve surfaces for varying sealing pressure bias as a function of said condition of operation to minimize leakage and said cylinder member having means providing an engaging pressure proportional to cylinder pressure, said signal means providing a signal varying as a function of the differential pressure in said high and low pressure ports and said control means supplying a bias fluid pressure to said bias fluid motor means for providing a biasing force decreasing with increasing differential pressure.

5. The invention defined in claim 4 and said signal means also including speed governor means operably connected to said members for providing a signal varying as a function of the relative speed of said members and said control means supplying a bias pressure varying as a function of displacement and speed to said bias motor means for providing a biasing force also increasing with increasing speed.

6. The invention defined in claim 4 and displacement varying means operatively connected to said reciprocating means for varying displacement of said piston and cylinder; said signal means also operatively connected to said displacement varying means for providing a signal varying as a function of displacement and said control means supplying a bias pressure varying as a function of differential pressure and displacement to said bias motor means for providing a bias force decreasing with increasing differential pressure and increasing with increasing displacement.

7. The invention defined in claim 6 and said signal means also including speed governor means operably connected to said members for providing a signal varying as a function of the relative speed of said members and said control means supplying a bias pressure varying as a function of displacement and speed to said bias motor means for providing a biasing force also increasing with increasing speed.

8. In a hydrostatic pump or motor unit; a housing; a port member having a first valve surface; a high pressure port and a low pressure port in said first valve surface; a cylinder member having a cylinder, a second valve surface in matching surface sealing contact at the interface with said first valve surface and an opening in said second valve surface to said cylinder; support and bearing means mounting said port me'rnber and said cylinder member in said housing for relative rotary and axial movement of said port member and said cylinder member toward each other for varying pressure continuous sealing engagement of said valve surfaces to control interface leakage of said opening being alternately connecting with said high and low pressure ports during said relative .rotation of said members; a piston in said cylinder; reciprocating means operably connected to said piston and said members for reciprocating said piston in said cylinder responsive to said relative rotation of said members; closed expansible chamber fluid bias motor means having relatively movable parts moved by fluid under pressure, one part operatively connected to said port member and the other part operatively connected to said cylinder member and operated by fluid bias pressure supplied to said closed expansible chamber to bias said valve surfaces of said members into sealing engagement; said housing enclosing the assembly of said piston, said cylinder member and said port member and collecting leakage fluid from said assembly; drain means operative to drain said leakage from said housing to provide a dry housing; signal means providing a signal varying as a function of a condition of operation of the unit varying with said interface leakage and control means operatively connected to said bias motor means and said signal means to supply a bias fluid pressure in said bias motor means varying as a function of said condition of operation to control the bias force between said valve surfaces for varying sealing pressure bias as a function of said condition of operation to minimize leakage and displacement varying means operatively connected to said reciprocating means for varying the displacement of said piston and cylinder; said signal means operatively connected to said displacement varying means for providing a signal varying as a function of displacement and said control means supplying a bias fluid pressure to said bias fluid motor means for providinga biasing force increasing with increasing displacement.

9. The invention defined in claim 8 and said signal means also including speed governor means operably connected to said members for providing a signal varying as a function of the relative speed of said members and said control means supplying a bias pressure varying as a function of displacement and speed to said bias motor means for providing a biasing force also increasing with increasing speed.

10. In a hydrostatic pump or motor unit; a port member having a first valve surface; a high pressure port and a low pressure port in said first valve surface; a cylinder member having a cylinder, a second valve surface in matching surface sealing contact at the interface with said first valve surface and an opening in said second valve surface to said cylinder; support and bearing means mounting said port member and said cylinder member for relative rotary and axial movement of said port member and said cylinder member toward each other for varying pressure continuous sealing engagement of said valve surfaces to control interface leakage and said opening being alternately connecting with said high and low pressure ports during said relative rotation of said members; a piston in said cylinder; reciprocating means operably connected to said piston and said members for reciprocating said piston in said cylinder responsive to said relative rotation of said members; expansible chamber fluid bias motor means operatively connected to said members and operated by fluid bias pressure to bias said valve surfaces of said members into sealing engagement; pressure signal means operatively connected to said high pressure port providing a signal varying as a function of the high pressure which varies with said interface leakage; speed signal means operatively connected to said members providing a speed signal varying as a function of the relative .rotary speed of said members and control means operatively connected to said bias motor means, said pressure signal means andfsaid speed signal means to supply a bias fluid pressure to said bias motor means varying as a function of said high pressure and said relative speed to control the bias force between said valve surfaces for varying sealing pressure bias as a function of said high pressure and relative speed to minimize leakage.

11. The invention defined in claim 10 and said bias pressure in said bias motor providing a bias force between said valve surfaces increasing with increasing speed and decreasing with increasing high pressure.

12. In a hydrostatic pump or motor unit; a port member having a first valve surface; a high pressure port and a low pressure port in said first valve surface; a cylinder member having a cylinder, a second valve surface in matching surface sealing contact at the interface with said first valve surface and an opening in said second valve surface to said cylinder; support and bearing means mounting said port member and said cylinder member for relative rotary and axial movement of said port member and said cylinder member toward each other for varying pressure continuing sealing-engagement of said valve surfaces to controlinterface leakage and said opening being alternately connecting with said high and low pressure ports during said relative rotation of said members; a piston in said cylinder; reciprocating means'operably connected to said piston and said members for reciprocating said piston in said cylinder responsive to said relative rotation of said members; displacement varying means operatively connected to said reciprocating means to vary the displacement of said piston and cylinder; displacement signal means operatively connected to said displacement varying means to provide a signal varying as a function of displacement; expansible chamber fluid bias motor means operatively connected to said members and operated by fluid bias pressure to bias said valve surfaces of said members into sealing engagement; signal means operatively connected to said high pressure port pro viding a signal varying as a function of the high pressure which varies with said interface leakage and control means operatively connected to said bias motor means, said signal means and said displacement signal means to supply a bias fluid pressure to said bias motor means varying as a function of said high pressure and said displacement to control the bias force between said valve surfaces for varying sealing pressure bias as a function of said high pressure and displacement to minimize leakage.

13. The invention defined in claim 12 and speed signal means operatively connected to said members to provide a speed signal varying as a function of the relative speed of said members; said control means operatively connected to said speed signal means and providing a bias pressure varying with high pressure, displacement and the relative speed of saidmembers and said bias motor means varying valve surface sealing pressure bias as a function of high pressure, displacement and relative rotary speed.

14. The invention defined in claim 13 and said bias force increasing with increasing speed and displacement and decreasing with increasing high pressure.

15. ln a hydrostatic pump or motor unit; a port member having a first valve surface, a high pressure port and a low pressure port in said first valve surface; a cylinder member having a cylinder, a second valve surface in matching surface sealing contact at the interface with said first valve surface and an opening in said second valve surface to said cylinder; support and bearing means mounting said port member and said cylinder member for relative rotary and axial movement of said port member and said cylinder member toward each other for varying pressure continuous sealing engagement of said valve surfaces to control interface leakage and said opening being alternately connected with said high and low pressure ports during said relative rotation of said members; a piston in said cylinder; reciprocating means operatively connected to said piston and said members for reciprocating said piston in said cylinder responsive to said relative rotation of said members; displacement varying means operatively connected to said reciprocating means to vary the displacement of said piston and cylinder; expansible chamber fluid bias motor means operatively connected to said members and operated by fluid bias pressure to bias said valve surfaces of said members into sealing eng'agement; signal means operatively connected to said displacement varying means providing a signal varying as a function of the displacement which varies with said interface leakage and control means operatively connected to said bias motor means and said signal means to supply a bias fluid pressure in said bias motor means varying as a function ofdisplacement to control the bias force between said valve surfaces for varying sealing pressure bias'as a function of displacement to minimize leakage.

16. The invention defined in claim and speed signal means operatively connected to said members providing a speed signal varying as a function of rotary speed and said control means being operatively connected to said speed signal means to supply bias pressure varying with displacement and relative speed.

17. The invention defined in claim 16 and said bias pressure in said bias motor providing a bias force between said valve surfaces increasing with increasing displacement and increasing speed.

18. In a hydrostatic pump or motor unit; a housing; a port structure having a first valve surface; a high pressure port and a low pressure port in said first valve surface; a cylinder structure having a cylinder, a second valve surface in matching surface sealing contact at the interface with said first valve surface and an opening in said second valve surface to said cylinder; support and bearing means fixing one structure in said housing and mounting the other structure in said housing for rotary and axial movement of said other structure toward said one structure for varying pressure continuous sealing engagement of said valve surfaces to control interface leakage and said opening being alternately connected with said high and low pressure ports during said relative rotation of said structures; a piston in said cylinder; reciprocating means operably connected to said piston and said structures for reciprocating said piston in said cylinder responsive to said relative rotation of said structures; fluid bias motor means for biasing said other structure toward said one structure providing varying pressure sealing engagement of said surfaces; :1 source of fluid under pressure; governor valve means mounted on said other structure for rotation with said other structure having an inlet port and an exhaust port exhausting fluid externally of said other structure and having an exhaust flow capacity variable to a maximum value regulating the pressure in said inlet port as a function of the speed of rotation of said other structure and exhausting excess fluid through said exhaust port externally of said other structure; a supply passage having a restriction limiting flow to less than said maximum value and connecting said source through said other structure to said inlet port and having the pressure between said restriction and inlet port substantially the same as the inlet port pressure regulated as a function of speed; and said supply passage from a point between said restriction and inlet port being connected to said bias motor.

19. The invention defined in claim 18 and said bias motor having concentric cylindrical surface means on each of said structures and first and second annular walls closely axially spaced slidably sealed between said concentric cylindrical surfaces forming a bias motor chamber therein and securing means connecting the first annular wall to one structure and the second annular wall to the other structure for relative axial movement of said structures for varying the pressure of said sealing engagement with pressure in said chamber of said bias motor.

20. The invention defined in claim 18 and said bias motor having a sleeve having an external cylinderical surface fixed to said one structure, a concentric internal cylindrical surface on said other member, a first annular wall slidably sealed between said cylindrical surfaces and axially fixed to said one structure and a sec- 0nd annular wall slidably sealed between said cylindrical surfaces and axially fixed to said other structure closely adjacent said first annular wall providing an expansible chamber therebetween; said supply passage being connected from said source through said one stationary structure to said chamber, through said chamber to said other structure and through said other structure to said inlet port with said restriction being in the connection from said source to said chamber and said bias motor functioning as a motor and fluid transfer device.

21. The invention defined in claim 18 and said one structure including a shaft rotatably mounted and axially fixed in said housing; said other structure being fixed on said shaft for rotation with said shaft and for axial movement relative to said shaft; said bias motor having an external cylindrical surface on the external surface of said shaft, a concentric internal cylindrical surface on said other structure and a first and second annular wall slidably sealed between said concentric cylindrical surfaces with the first wall coaxially secured to said shaft and the second wall axially secured to said other structure closely adjacent each other providing an expansible chamber therebetween; said supply passage including a rotary transfer device being connected from said source by said rotary transfer device to said shaft, through said shaft to said chamber, through said chamber to said other structure and through said other structure to said inlet port with said restriction being between said source and said chamber.

22. The invention defined in claim 18 and said governor valve means having a radial bore, a valve control opening in said bore, valve chamber means providing a fluid chamber radially outward of said valve control opening connected to said inlet port, weight valve member means movably mounted in said bore for movement by centrifugal force as a function of rotary speed to close said control opening and fluid pressure in said valve chamber meansacting on said weight valve member means for movement as a function of pressure in said valve chamber to open said control opening to connect said valve chamber to said exhaust port to provide in said valve chamber and inlet port a pressure varying as a function of speed.

23. The invention defined in claim 18 and said governor valve means having a radial bore closed at the radial outer end, a valve seal surface radially inwardly of said closed end with a valve chamber therebetween connected to said inlet port, said exhaust port being in said bore radially inward of said seal surface, a weight valve member reciprocally mounted in said bore engaging said seal surface for closing said bore and opening for connecting said valve chamber to said exhaust port, a weight member reciprocally mounted in said bore inwardly of said weight valve member and a spring mounted in said bore between said weight member and weight valve member to provide a two step governor regulating pressure as a function of speed in two phases.

24. The invention defined in claim 18 and said governor valve means having a radial bore, a stationary valve member mounted in the outer portion of said bore having a valve control opening and radially outward of said valve control opening an enclosure providing a valve chamber, a weight valve member reciprocally mounted in said bore for movement by centrifugal force as a function of speed to close said control opening and fluid pressure in said valve chamber acting on said weight valve member to open said valve control opening to .connect said valve chamber to said exhaust port, said supply passage extending through said bore and said inlet port being a central passage radially through said weight valve member. a

25. In a hydrostatic pump or motor unit; a housing; a port member having a first valve surface; a high pressure port and a low pressure port in said first valve surface; a cylinder member having a cylinder, a second valve surface in matching surface sealing contact at the interface with said first valve surface and an opening in said second valve surface to said cylinder; support and bearing means mounting said port member and said cylinder member in said housing for relative rotary and axial movement of said port member and said cylinder member toward each other for relative rotation and sealing engagement of said valve surfaces under a normal varying hold-down sealing force to control interface leakage and said opening being alternately connecting with said high and low pressure ports during said relative rotation of saidmembers; a piston in said cylinder; reciprocating means operably connected to said piston and said members for reciprocating said piston in said cylinder responsive to said relative rotation of said members; expansible chamber fluid bias motor means having relatively movable parts moved by fluid under pressure, one part operatively connected to said port member and the other part operatively connected to said cylinder member and operated by fluid bias pressure supplied to said closed expansible chamber to bias said valve surfaces of said members into sealing engagement; signal means providing a signal varying as a function of a condition of operation of the unit varying with said interface leakage and pressure regulator means operatively connected to said bias motor means and said signal means and controlled by said signal varying as a function of a condition of operation of the unit to regulate and to supply a bias fluid pressure in said bias motor means varying as another function of said signal to provide the additional hold-down sealing force required to minimize leakage and friction between said valve surfaces and to provide a bias force between said valve surfaces for varying the total holddown sealing force to minimize leakage and friction between said valve surfaces.

26. In a hydrostatic pump or motor unit; a housing; a port member having a first valve surface; a high pressure port providing a high pressure operating condition and a low pressure port in said first valve surface; a cylinder member having a cylinder, a second valve surface in matching surface sealing contact at the interface with said first valve surface and an opening in said second valve surface to said cylinder; support and bearing means mounting said port member and said cylinder member in said housing for relative rotary movement providing a rotary speed operating condition and axial movement of said port member and said cylinder mem ber toward each other for continuous sealing engagement of said valve surfaces under a normal varying hold-down sealing force to control interface leakage and said opening. being alternately connecting with said high and low 'pressure'pons during said relative rotation of said members; a piston in said cylinder; reciprocating means operably connected to said piston and said members for variably reciprocating said piston in said cylinder responsive to said relative rotation of said members to provide variable displacement and a displacement operating condition closed expansible chamber fluid bias motor means having relatively movable parts moved by fluid under pressure, one part operatively connected to said port member and the other part operatively connected to said cylinder member and operated by fluid bias pressure supplied to said closed expansible chamber to bias said valve surfaces of said members into sealing engagement; first signal means providing a first signal varying as a function of one condition of operation of the unit varying with said interface leakage; second signal means providing a second signal varying as a function of another condition of operation of the unit varying with said interface leakage and pressure regulator control means operatively connected to said bias motor means and said first and second signal means and controlled by said first and second signals to regulate and to supply a bias fluid pressure in said bias motor means varying as a function of both said signals to provide the additional hold-down sealing force required to minimize leakage and friction between said valve surfaces to provide a proportional bias force between said valve surfaces for varying the total hold-down sealing force to minimize leakage and friction between said valve surfaces.

27. The invention defined in claim 26 and said first signal means being responsive to said high pressure operating condition and said second signal means being responsive to said rotary speed operating condition.

28. The invention defined in claim 26 and said first signal means being responsive to said high pressure operating condition and said second signal means being responsive to said displacement operating condition.

29. The invention defined in claim 26 and said first signal means being responsive to said rotary speed operating condition and said second signal means being responsive to said displacement operating condition.

30. The invention defined in claim 29 and a third signal means providing a third signal varying as a function of said high pressure operating condition and said pressure regulator means also operatively connected to said third signal means and responsive to said high pressure operating condition.

- -i r UNITED1STATES PATENT OFFICE 569 CERTIFICATE OF CORRECTION Patent No. 3,-8;O,715 e Dated May 14' 1974 lnventofls) P. Week It is certified that error appears in the above-identified p aten t v and that said Lettets Pat ent are hereby corrected as shown below:

xn-theclaims; claim 1. com ie. line 30,"'movab1e" shoiald be movably claim 4, column 19, line 45,- delete "a" first occurrence claim 8, column 20, line- 35, "of" should be Signed sealed e tis 3rd dayv of December 1974.

(SEAL) AtteSt: v I

c MARSHALL, 1mm Commissioner of Patents McCOY M. GIBSON R,

Attesting -Officer y. 

1. In a hydrostatic pump or motor unit; a housing; cylinder barrel means rotatably mounted in said housing for rotation about an axis and axially movable mounted for limited axial and transverse seating movement; a first transverse valve surface on said housing having a first and a second port for high and low pressure; a second transverse valve surface on said barrel means in continuous rotary surface seating engagement with said first surface providing an interface seal; a plurality of cylinders in said barrel means each having a third port connected to said second surface and alternately being connected to said first and second ports and said ports being sealed by said interface seal during rotation of said barrel means; pistons in said cylinders; means to reciprocate said pistons in said cylinders; bias motor means having an axially fixed member with an external concentric cylindrical wall axially fixed relative to said housing and an internal concentric cylindrical wall on said barrel means and two axially short annular piston members each having inner and outer diameter seals in contact respectively with said external and internal concentric cylindrical surfaces, one piston member being adjacent said interface seal, and freely slidable on said external cylindrical wall; the other piston member being remote from said interface seal and freely slidable on said internal cylindrical wall; means on said barrel means to limit axial movement of the annular piston member adjacent said interface seal relative to said barrel means toward said interface seal and means on said axially fixed member to limit axial movement of the other annular piston member remote from said interface seal relative to said axially fixed member away from said interface seal and said annular piston members being closely axially spaced to provide an axially short expansible chamber for fluid having minimal fluid contact with said concentric cylindrical walls responsive to fluid pressure in said chamber to bias said barrel means for axial movement against said housing for pressure engagement of said interface seal permitting seating movement and control means to supply a bias control pressure to said chamber of said bias motor means.
 2. The invention defined in claim 1 and said axially fixed member with an external cylindrical surface being a sleeve fixed to said housing and projecting in spaced relation into said external cylindrical surface providing said concentric cylindrical surfaces.
 3. The invention defined in claim 1 and said axially fixed member with an external cylindrical wall being a shaft of said barrel means rotatably mounted and axially fixed relative to said housing and said barrel means including a barrel member secured to said shaft to rotate with said shaft and to permit relative axial and transverse seating movement.
 4. In a hydrostatic pump or motor unit; a housing; a port member having a first valve surface; a high pressure port and a low pressure port in said first valve surface; a cylinder member having a cylinder, a second valve surface in matching surface sealing contact at the interface with said first valve surface and an opening in said second valve surface to said cylinder; support and bearing means mounting said port member and said cylinder member in said housing for relative rotary and axial movement of said port member and said cylinder member toward each other for varying pressure continuous sealing engagement of said valve surfaces to control interface leakage and said opening being alternately connecting with said high and low pressure ports during said relative rotation of said members; a piston in said cylinder; reciprocating means operably connected to said piston and said members for reciprocating said piston in said cylinder responsive to said relative rotation of said members; closed expansible chamber fluid bias motor means having relatively movable parts moved by fluid under pressure, one part operatively connected to said port member and the other part operatively connected to said cylinder member and operated by fluid bias pressure supplied to said closed expansible chamber to bias said valve surfaces of said members into sealing engagement; said housing enclosing the assembly of said piston, said cylinder member and said port member and collecting leakage fluid from said assembly; drain means operative to drain said leakage from said housing to provide a dry housing; a signal means providing a signal varying as a function of a condition of operation of the unit varying with said interface leakage and control means operatively connected to said bias motor means and said signal means to supply a bias fluid pressure in said bias motor means varying as a function of said condition of operation to control the bias force between said valve surfaces for varying sealing pressure bias as a function of said condition of operation to minimize leakage and said cylinder member having means providing an engaging pressure proportional to cylinder pressure, said signal means providing a signal varying as a function of the differential pressure in said high and low pressure ports and said control means supplying a bias fluid pressure to said bias fluid motor means for providing a biasing force decreasing with increasing differential pressure.
 5. The invention defined in claim 4 and said signal means also including speed governor means operably connected to said members for providing a signal varying as a function of the relative speed of said members and said control means supplying a bias pressure varying as a function of displacement and speed to said bias motor means for providing a biasing force also increasing with increasing speed.
 6. The invention defined in claim 4 and displacement varying means operatively connected to said reciprocating means for varying displacement of said piston and cylinder; said signal means also operatively connected to said displacement varying means for providing a signal varying as a function of displacement and said control means supplying a bias pressure varying as a function of differential pressure and displacement to said bias motor means for providing a bias force decreasing with increasing differential pressure and increasing with increasing displacement.
 7. The invention defined in claim 6 and said signal means also including speed governor means operably connected to said members for providing a signal varying as a function of the relative speed of said members and said control means supplying a bias pressure varying as a function of displacement and speed to said bias motor means for providing a biasing force also increasing with increasing speed.
 8. In a hydrostatic pump or motor unit; a housing; a port member having a first valve surface; a high pressure port and a low pressure port in said first valve surface; a cylinder member having a cylinder, a second valve surface in matching surface sealing contact at the interface with said first valve surface and an opening in said second valve surface to said cylinder; support and bearing means mounting said port member and said cylinder member in said housing for relative rotary and axial movement of said port member and said cylinder member toward each other for varying pressure continuous sealing engagement of said valve surfaces to control interface leakage of said opening being alternately connecting with said high and low pressure ports during said relative rotation of said members; a piston in said cylinder; reciprocating means operably connected to said piston and said members for reciprocating said piston in said cylinder responsive to said relative rotation of said members; closed expansible chamber fluid bias motor means having relatively movable parts moved by fluid under pressure, one part operatively connected to said port member and the other part operatively connected to said cylinder member and operated by fluid bias pressure supplied to said closed expansible chamber to bias said valve surfaces of said members into sealing engagement; said housing enclosing the assembly of said piston, said cylinder member and said port member and collecting leakage fluid from said assembly; drain means operative to drain said leakage from said housing to provide a dry housing; signal means providing a signal varying as a function of a condition of operation of the unit varying with said interface leakage and control means operatively connected to said bias motor means and said signal means to supply a bias fluid pressure in said bias motor means varying as a function of said condition of operation to control the bias force between said valve surfaces for varying sealing pressure bias as a function of said condition of operation to minimize leakage and displacement varying means operatively connected to said reciprocating means for varying the displacement of said piston and cylinder; said signal means operatively connected to said displacement varying means for providing a signal varying as a function of displacement and said control means supplying a bias fluid pressure to said bias fluid motor means for providing a biasing force increasing with increasing displacement.
 9. The invention defined in claim 8 and said signal means also including speed governor means operably connected to said members for providing a signal varying as a function of the relative speed of said members and said control means supplying a bias pressure varying as a function of displacement and speed to said bias motor means for providing a biasing force also increasing with increasing speed.
 10. In a hydrostatic pump or motor unit; a port member having a first valve surface; a high pressure port and a low pressure port in said first valve surface; a cylinder member having a cylinder, a second valve surface in matching surface sealing contact at the interface with said first valve surface and an opening in said second valve surface to said cylinder; support and bearing means mounting said port member and said cylinder member for relative rotary and axial movement of said port member and said cylinder member toward each other for varying pressure continuous sealing engagement of said valve surfaces to control interface leakage and said opening being alternately connecting with said high and low pressure ports during said relative rotation of said members; a piston in said cylinder; reciprocating means operably connected to said piston and said members for reciprocating said piston in said cylinder responsive to said relative rotation of said members; expansible chamber fluid bias motor means operatively connected to said members and operated by fluid bias pressure to bias said valve surfaces of said members into sealing engagement; pressure signal means operatively connected to said high pressure port providing a signal varying as a function of the high pressure which varies with said interface leakage; speed signal means operatively connected to said members providing a speed signal varying as a function of the relative rotary speed of said members and control means operatively connected to said bias motor means, said pressure signal means and said speed signal means to supply a bias fluid pressure to said bias motor means varying as a function of said high pressure and said relative speed to control the bias force between said valve surfaces for varying sealing pressure bias as a function of said high pressure and relative speed to minimize leakage.
 11. The invention defined in claim 10 and said bias pressure in said bias motor providing a bias force between said valve surfaces increasing with increasing speed and decreAsing with increasing high pressure.
 12. In a hydrostatic pump or motor unit; a port member having a first valve surface; a high pressure port and a low pressure port in said first valve surface; a cylinder member having a cylinder, a second valve surface in matching surface sealing contact at the interface with said first valve surface and an opening in said second valve surface to said cylinder; support and bearing means mounting said port member and said cylinder member for relative rotary and axial movement of said port member and said cylinder member toward each other for varying pressure continuing sealing engagement of said valve surfaces to control interface leakage and said opening being alternately connecting with said high and low pressure ports during said relative rotation of said members; a piston in said cylinder; reciprocating means operably connected to said piston and said members for reciprocating said piston in said cylinder responsive to said relative rotation of said members; displacement varying means operatively connected to said reciprocating means to vary the displacement of said piston and cylinder; displacement signal means operatively connected to said displacement varying means to provide a signal varying as a function of displacement; expansible chamber fluid bias motor means operatively connected to said members and operated by fluid bias pressure to bias said valve surfaces of said members into sealing engagement; signal means operatively connected to said high pressure port providing a signal varying as a function of the high pressure which varies with said interface leakage and control means operatively connected to said bias motor means, said signal means and said displacement signal means to supply a bias fluid pressure to said bias motor means varying as a function of said high pressure and said displacement to control the bias force between said valve surfaces for varying sealing pressure bias as a function of said high pressure and displacement to minimize leakage.
 13. The invention defined in claim 12 and speed signal means operatively connected to said members to provide a speed signal varying as a function of the relative speed of said members; said control means operatively connected to said speed signal means and providing a bias pressure varying with high pressure, displacement and the relative speed of said members and said bias motor means varying valve surface sealing pressure bias as a function of high pressure, displacement and relative rotary speed.
 14. The invention defined in claim 13 and said bias force increasing with increasing speed and displacement and decreasing with increasing high pressure.
 15. In a hydrostatic pump or motor unit; a port member having a first valve surface, a high pressure port and a low pressure port in said first valve surface; a cylinder member having a cylinder, a second valve surface in matching surface sealing contact at the interface with said first valve surface and an opening in said second valve surface to said cylinder; support and bearing means mounting said port member and said cylinder member for relative rotary and axial movement of said port member and said cylinder member toward each other for varying pressure continuous sealing engagement of said valve surfaces to control interface leakage and said opening being alternately connected with said high and low pressure ports during said relative rotation of said members; a piston in said cylinder; reciprocating means operatively connected to said piston and said members for reciprocating said piston in said cylinder responsive to said relative rotation of said members; displacement varying means operatively connected to said reciprocating means to vary the displacement of said piston and cylinder; expansible chamber fluid bias motor means operatively connected to said members and operated by fluid bias pressure to bias said valve surfaces of said members into sealing engagement; signal means operatively connected tO said displacement varying means providing a signal varying as a function of the displacement which varies with said interface leakage and control means operatively connected to said bias motor means and said signal means to supply a bias fluid pressure in said bias motor means varying as a function of displacement to control the bias force between said valve surfaces for varying sealing pressure bias as a function of displacement to minimize leakage.
 16. The invention defined in claim 15 and speed signal means operatively connected to said members providing a speed signal varying as a function of rotary speed and said control means being operatively connected to said speed signal means to supply bias pressure varying with displacement and relative speed.
 17. The invention defined in claim 16 and said bias pressure in said bias motor providing a bias force between said valve surfaces increasing with increasing displacement and increasing speed.
 18. In a hydrostatic pump or motor unit; a housing; a port structure having a first valve surface; a high pressure port and a low pressure port in said first valve surface; a cylinder structure having a cylinder, a second valve surface in matching surface sealing contact at the interface with said first valve surface and an opening in said second valve surface to said cylinder; support and bearing means fixing one structure in said housing and mounting the other structure in said housing for rotary and axial movement of said other structure toward said one structure for varying pressure continuous sealing engagement of said valve surfaces to control interface leakage and said opening being alternately connected with said high and low pressure ports during said relative rotation of said structures; a piston in said cylinder; reciprocating means operably connected to said piston and said structures for reciprocating said piston in said cylinder responsive to said relative rotation of said structures; fluid bias motor means for biasing said other structure toward said one structure providing varying pressure sealing engagement of said surfaces; a source of fluid under pressure; governor valve means mounted on said other structure for rotation with said other structure having an inlet port and an exhaust port exhausting fluid externally of said other structure and having an exhaust flow capacity variable to a maximum value regulating the pressure in said inlet port as a function of the speed of rotation of said other structure and exhausting excess fluid through said exhaust port externally of said other structure; a supply passage having a restriction limiting flow to less than said maximum value and connecting said source through said other structure to said inlet port and having the pressure between said restriction and inlet port substantially the same as the inlet port pressure regulated as a function of speed; and said supply passage from a point between said restriction and inlet port being connected to said bias motor.
 19. The invention defined in claim 18 and said bias motor having concentric cylindrical surface means on each of said structures and first and second annular walls closely axially spaced slidably sealed between said concentric cylindrical surfaces forming a bias motor chamber therein and securing means connecting the first annular wall to one structure and the second annular wall to the other structure for relative axial movement of said structures for varying the pressure of said sealing engagement with pressure in said chamber of said bias motor.
 20. The invention defined in claim 18 and said bias motor having a sleeve having an external cylinderical surface fixed to said one structure, a concentric internal cylindrical surface on said other member, a first annular wall slidably sealed between said cylindrical surfaces and axially fixed to said one structure and a second annular wall slidably sealed between said cylindrical surfaces and axially fixed to said other structure closely adjacent said fiRst annular wall providing an expansible chamber therebetween; said supply passage being connected from said source through said one stationary structure to said chamber, through said chamber to said other structure and through said other structure to said inlet port with said restriction being in the connection from said source to said chamber and said bias motor functioning as a motor and fluid transfer device.
 21. The invention defined in claim 18 and said one structure including a shaft rotatably mounted and axially fixed in said housing; said other structure being fixed on said shaft for rotation with said shaft and for axial movement relative to said shaft; said bias motor having an external cylindrical surface on the external surface of said shaft, a concentric internal cylindrical surface on said other structure and a first and second annular wall slidably sealed between said concentric cylindrical surfaces with the first wall coaxially secured to said shaft and the second wall axially secured to said other structure closely adjacent each other providing an expansible chamber therebetween; said supply passage including a rotary transfer device being connected from said source by said rotary transfer device to said shaft, through said shaft to said chamber, through said chamber to said other structure and through said other structure to said inlet port with said restriction being between said source and said chamber.
 22. The invention defined in claim 18 and said governor valve means having a radial bore, a valve control opening in said bore, valve chamber means providing a fluid chamber radially outward of said valve control opening connected to said inlet port, weight valve member means movably mounted in said bore for movement by centrifugal force as a function of rotary speed to close said control opening and fluid pressure in said valve chamber means acting on said weight valve member means for movement as a function of pressure in said valve chamber to open said control opening to connect said valve chamber to said exhaust port to provide in said valve chamber and inlet port a pressure varying as a function of speed.
 23. The invention defined in claim 18 and said governor valve means having a radial bore closed at the radial outer end, a valve seal surface radially inwardly of said closed end with a valve chamber therebetween connected to said inlet port, said exhaust port being in said bore radially inward of said seal surface, a weight valve member reciprocally mounted in said bore engaging said seal surface for closing said bore and opening for connecting said valve chamber to said exhaust port, a weight member reciprocally mounted in said bore inwardly of said weight valve member and a spring mounted in said bore between said weight member and weight valve member to provide a two step governor regulating pressure as a function of speed in two phases.
 24. The invention defined in claim 18 and said governor valve means having a radial bore, a stationary valve member mounted in the outer portion of said bore having a valve control opening and radially outward of said valve control opening an enclosure providing a valve chamber, a weight valve member reciprocally mounted in said bore for movement by centrifugal force as a function of speed to close said control opening and fluid pressure in said valve chamber acting on said weight valve member to open said valve control opening to connect said valve chamber to said exhaust port, said supply passage extending through said bore and said inlet port being a central passage radially through said weight valve member.
 25. In a hydrostatic pump or motor unit; a housing; a port member having a first valve surface; a high pressure port and a low pressure port in said first valve surface; a cylinder member having a cylinder, a second valve surface in matching surface sealing contact at the interface with said first valve surface and an opening in said second valve surface to said cylinder; support and bearing means mounting said port member and said cylinder member in said housing for relative rotary and axial movement of said port member and said cylinder member toward each other for relative rotation and sealing engagement of said valve surfaces under a normal varying hold-down sealing force to control interface leakage and said opening being alternately connecting with said high and low pressure ports during said relative rotation of said members; a piston in said cylinder; reciprocating means operably connected to said piston and said members for reciprocating said piston in said cylinder responsive to said relative rotation of said members; expansible chamber fluid bias motor means having relatively movable parts moved by fluid under pressure, one part operatively connected to said port member and the other part operatively connected to said cylinder member and operated by fluid bias pressure supplied to said closed expansible chamber to bias said valve surfaces of said members into sealing engagement; signal means providing a signal varying as a function of a condition of operation of the unit varying with said interface leakage and pressure regulator means operatively connected to said bias motor means and said signal means and controlled by said signal varying as a function of a condition of operation of the unit to regulate and to supply a bias fluid pressure in said bias motor means varying as another function of said signal to provide the additional hold-down sealing force required to minimize leakage and friction between said valve surfaces and to provide a bias force between said valve surfaces for varying the total hold-down sealing force to minimize leakage and friction between said valve surfaces.
 26. In a hydrostatic pump or motor unit; a housing; a port member having a first valve surface; a high pressure port providing a high pressure operating condition and a low pressure port in said first valve surface; a cylinder member having a cylinder, a second valve surface in matching surface sealing contact at the interface with said first valve surface and an opening in said second valve surface to said cylinder; support and bearing means mounting said port member and said cylinder member in said housing for relative rotary movement providing a rotary speed operating condition and axial movement of said port member and said cylinder member toward each other for continuous sealing engagement of said valve surfaces under a normal varying hold-down sealing force to control interface leakage and said opening being alternately connecting with said high and low pressure ports during said relative rotation of said members; a piston in said cylinder; reciprocating means operably connected to said piston and said members for variably reciprocating said piston in said cylinder responsive to said relative rotation of said members to provide variable displacement and a displacement operating condition closed expansible chamber fluid bias motor means having relatively movable parts moved by fluid under pressure, one part operatively connected to said port member and the other part operatively connected to said cylinder member and operated by fluid bias pressure supplied to said closed expansible chamber to bias said valve surfaces of said members into sealing engagement; first signal means providing a first signal varying as a function of one condition of operation of the unit varying with said interface leakage; second signal means providing a second signal varying as a function of another condition of operation of the unit varying with said interface leakage and pressure regulator control means operatively connected to said bias motor means and said first and second signal means and controlled by said first and second signals to regulate and to supply a bias fluid pressure in said bias motor means varying as a function of both said signals to provide the additional hold-down sealing force required to minimize leakage and friction between said valve surfaces tO provide a proportional bias force between said valve surfaces for varying the total hold-down sealing force to minimize leakage and friction between said valve surfaces.
 27. The invention defined in claim 26 and said first signal means being responsive to said high pressure operating condition and said second signal means being responsive to said rotary speed operating condition.
 28. The invention defined in claim 26 and said first signal means being responsive to said high pressure operating condition and said second signal means being responsive to said displacement operating condition.
 29. The invention defined in claim 26 and said first signal means being responsive to said rotary speed operating condition and said second signal means being responsive to said displacement operating condition.
 30. The invention defined in claim 29 and a third signal means providing a third signal varying as a function of said high pressure operating condition and said pressure regulator means also operatively connected to said third signal means and responsive to said high pressure operating condition. 